Michelle A. Manzo

Performance characterization of a lithium-ion gel polymer battery power supply system for an unmanned aerial vehicle

ABSTRACT Unmanned aerial vehicles (UAVs) are currently under development for NASA missions, earth sciences, aeronautics, the military, and commercial applications. The design of an all electric power and propulsion system for small UAVs was the focus of a detailed study. Currently, many of these small vehicles are powered by primary (nonrechargeable) lithium-based batteries. While this type of battery is capable of satisfying some of the mission needs, a secondary (rechargeable) battery power supply system that can provide the same functionality as the current system at the same or lower system mass and volume is desired. A study of commercially available secondary battery cell technologies that could provide the desired performance characteristics was performed. Due to the strict mass limitations and wide operating temperature requirements of small UAVs, the only viable cell chemistries were determined to be lithium-ion liquid electrolyte systems and lithium-ion gel polymer electrolyte systems. Two lithium-ion gel polymer cell designs were selected as candidates and were tested using potential load profiles for UAV applications. Because lithium primary batteries have a higher specific energy and energy density, for the same mass and volume allocation, the secondary batteries resulted in shorter flight times than the primary batteries typically provide. When the batteries were operated at lower ambient temperatures (0 to -20 °C), flight times were even further reduced. Despite the reduced flight times demonstrated, for certain UAV applications, the secondary batteries operated within the acceptable range of flight times at room temperature and above. The results of this testing indicate that a secondary battery power supply system can provide some benefits over the primary battery power supply system. A UAV can be operated for hundreds of flights using a secondary battery power supply system that provides the combined benefits of rechargeability and an inherently safer chemistry.

An Overview of Power Capability Requirements for Exploration Missions

Advanced power is one of the key capabilities that will be needed to achieve NASA’s missions of exploration and scientific advancement. Significant gaps exist in advanced power capabilities that are on the critical path to enabling human exploration beyond Earth orbit and advanced robotic exploration of the solar system. Focused studies and investment are needed to answer key development issues for all candidate technologies before downselection. The viability of candidate power technology alternatives will be a major factor in determining what exploration mission architectures are possible. Achieving the capabilities needed to enable the CEV, Moon and Mars missions is dependent on adequate funding. Focused investment in advanced power technologies for human and robotic exploration missions is imperative now to reduce risk and to make informed decisions on potential exploration mission decisions beginning in 2008. This investment would begin the long leadtime needed to develop capabilities for human exploration missions in the 2015-2030 timeframe. This paper identifies some of the key technologies that will be needed to fill these power capability gaps. Recommendations are offered to address capability gaps in advanced power for Crew Exploration Vehicle (CEV) power, surface nuclear power systems, surface mobile power systems, high efficiency power systems, and space transportation power systems. These capabilities fill gaps that are on the critical path to enabling robotic and human exploration missions. The recommendations address the following critical technology areas: Energy Conversion, Energy Storage, and Power Management and Distribution.

Energy Storage: Batteries and Fuel Cells for Exploration

NASAs Vision for Exploration requires safe, human-rated, energy storage technologies with high energy density, high specific energy and the ability to perform in a variety of unique environments. The Exploration Technology Development Program is currently supporting the development of battery and fuel cell systems that address these critical technology areas. Specific technology efforts that advance these systems and optimize their operation in various space environments are addressed in this overview of the Energy Storage Technology Development Project. These technologies will support a new generation of more affordable, more reliable, and more effective space systems.

Performance and Comparison of Lithium-Ion Batteries Under Low-Earth-Orbit Mission Profiles

Abstract The performance of two 28 V, 25 Ah lithium-ion batteries is being evaluated under low-Earth-orbit mission profiles for satellite and orbiter applications. These space flight-qualified batteries were designed and fabricated by Lithion, Inc. (Yardney Technical Products) for the 2001 Mars Surveyor Program Lander, the first major NASA mission that baselined lithium-ion battery technology. Lithium-ion battery chemistry was an enabling technology for the mission because of its ability to provide low temperature operation in a lightweight and compact battery design. The Mars Surveyor Program mission was cancelled before launch, however, the Lander batteries had already been built and flight-qualified. Lithium-ion batteries are being baselined for increasingly more missions, including missions in low-Earth-orbit and geosynchronous orbit. These mission conditions are more challenging for lithium-ion batteries than a short mission on Mars. Many more cycles are required for operation in low-Earth-orbit and a much longer calendar life is required for operation in either low-Earth-orbit or geosynchronous orbit. A ground test program was established that utilized the Lander batteries from the original mission to demonstrate performance and life under various mission conditions. This paper presents results of the low-Earth-orbit (LEO) portion of the testing that is being conducted at NASA Glenn Research Center (GRC) and NASA Jet Propulsion Laboratory (JPL). The batteries discussed are currently undergoing life testing and have each achieved over 12,000 cycles to 40 percent depth-of-discharge. Each battery is cycling at a different temperature, one at 23 °C and the other at 0 °C. In addition to cycling under low-Earth-orbit conditions, the batteries have been characterized at 500 to 1000 cycle intervals throughout the life testing to observe their capacity and DC impedance changes. Because the batteries are not equipped with cell balancing electronics, cell balancing is manually performed on each battery when cell voltage dispersion exceeds the established threshold. The performance of the batteries will be discussed individually and their performance relative to each other at the different test conditions will be compared.

Nickel-hydrogen capacity loss on storage

A controlled experiment evaluating the capacity loss experienced by nickel electrodes stored under various conditions of temperature, hydrogen pressure, and electrolyte concentration was conducted using nickel electrodes from four different manufacturers. It was found that capacity loss varied with regard to hydrogen pressure and storage temperature, as well as with regard to electrode manufacturing processes. Impedance characteristics were monitored and found to be indicative of electrode manufacturing processes and capacity loss. Cell testing to evaluate state-of-charge effects on capacity loss were inconclusive as no loss was sustained by the cells tested in this experiment.

The Effect of Variable End of Charge Battery Management on Small-Cell Batteries

ABSL Space Products is the world leading supplier of Lithium-ion batteries for space applications and has pioneered the use of small capacity COTS cells within large arrays. This small-cell approach has provided many benefits to space application designers through increased flexibility and reliability over more traditional battery designs. The ABSL 18650HC cell has been used in most ABSL space battery applications to date and has a recommended End Of Charge Voltage (EOCV) of 4.2V per cell. For all space applications using the ABSL 18650HC so far, this EOCV has been used at all stages of battery life from ground checkout to in orbit operations. ABSL and NASA have identified that, by using a lower EOCV for the same equivalent Depth Of Discharge (DOD), battery capacity fade could be reduced. The intention of this paper is to compare battery performance for systems with fixed and variable EOCV. In particular, the effect of employing the blanket value of 4.2V per cell versus utilizing a lower EOCV at Beginning Of Life (BOL) before gradually increasing it (as the effects of capacity fade drive the End Of Discharge Voltage closer to the acceptable system level minimum) is analyzed. Data is compared from ABSL in-house and NASA GRC tests that have been run under fixed and variable EOCV conditions. Differences in capacity fade are discussed and projections are made as to potential life extension capability by utilizing a variable EOCV strategy.

Characterization testing of a 40 ampere hour bipolar nickel-hydrogen battery

Abstract Extensive characterization testing has been done on a second 40 ampere hour (A h), 10-cell, bipolar nickel—hydrogen (Ni—H 2 ) battery to study the effects of operating parameters such as charge and discharge rates, temperature, and pressure on capacity, A h and watt hour (W h) efficiencies, end-of-charge (EOC), and mid-point discharge voltages. Testing to date has produced many interesting results, with the battery performing well throughout the test matrix except during the high-rate (5 C and 10 C ) discharges, where poorer than expected results were observed. The exact cause of this poor performance is, as yet, unknown. Small scale 2 in. × 2 in. battery tests are to be used in studying this problem. Low earth orbit (LEO) cycle life testing at a 40% depth of discharge (DOD) and 10 °C is scheduled to follow the characterization testing.